Electronic systems may comprise many electrically interconnected components, including circuit boards and associated connector assemblies. Typically, each board carries a portion of an electronic circuit and has a plurality of electrical terminals for connecting to the electrical terminals of other boards through the connector assemblies when the boards are inserted therein. Generally, each board is designed for insertion in only one uniquely associated connector assembly to prevent damage to the system as well as the board by means of mechanical or electrical keying arrangements.
Generally, mechanical keying arrangements prevent the complete insertion of an improper board into a connector assembly, whereas, electrical keying arrangements prevent the application of electrical signals to an improper board completely inserted in a connector assembly. However, there are systems in which the same set of connector assemblies must receive many groups of like type circuit boards, each group having a type of board which may be different from those in another group. One example would be a system for testing or modifying like types of circuit boards having erasable, programmable, ready-only memory units positioned thereon. Conventional keying arrangements would preclude such a system; however, it would still be highly desirable to prevent damage to the system as well as the boards when different types of circuit boards are concurrently inserted in an associated set of connector assemblies.